remote-mic/audio/ffmpeg.go

package audio

import (
	"os/exec"
	"fmt"
	"regexp"
	"runtime"
	"io"
)


type microphone struct {
	command *exec.Cmd
	audioStream io.Reader
	diagnosticOutput io.Reader
	Format string
	Device string
	Encoding Encoding
}

func NewMicrophone() (*microphone, error) {
	if runtime.GOOS != "darwin" {
		panic(fmt.Errorf("audio.microphone is only supported on macOS"))
	}
	format := "avfoundation"
	device, err := getMicDevice(format)
	if err != nil {
		return nil, err
	}
	return &microphone{
		Format: format,
		Device: device,
		Encoding: defaultEncoding,
	}, nil
}

func (m *microphone) Start() error {
	m.command = exec.Command("ffmpeg", "-re",
		"-f", m.Format,
		"-i", fmt.Sprintf(":%s", m.Device),
		"-f", m.Encoding.Codec,
		"-ar", fmt.Sprintf("%d", m.Encoding.Bitrate),
		"-ac", fmt.Sprintf("%d", m.Encoding.Channels),
		"-",
	)

	// these should never fail, unless you use the module incorrectly
	audioStream, err := m.command.StdoutPipe()
	if err != nil {
		panic(err)
	}
	diagnosticOutput, err := m.command.StderrPipe()
	if err != nil {
		panic(err)
	}

	m.audioStream, m.diagnosticOutput = audioStream, diagnosticOutput
	return m.command.Start()
}

func (m *microphone) Stop() error {
	return m.command.Process.Kill()
}

func (m *microphone) AudioStream() io.Reader {
	if m.audioStream == nil {
		panic(fmt.Errorf("AudioStream() called before Start()"))
	}
	return m.audioStream
}

func (m *microphone) DiagnosticOutput() io.Reader {
	if m.diagnosticOutput == nil {
		panic(fmt.Errorf("DiagnosticOutput() called before Start()"))
	}
	return m.diagnosticOutput
}

func getMicDevice(format string) (string, error) {
	cmd := exec.Command("ffmpeg",
		"-f", format,
		"-list_devices", "true",
		"-i", "\"\"",
	)
	// ignore error, this ffmpeg command returns exit status 1
	outputBytes, _ := cmd.CombinedOutput()
	output := string(outputBytes)
	parsedOutput := parseDeviceNumber(output)
	if parsedOutput == "" {
		return "", fmt.Errorf("Command: %s\nFailed to parse FFmpeg output:\n%s", cmd, output)
	}
	return parsedOutput, nil
}

func parseDeviceNumber(ffmpegOutput string) string {
	re := regexp.MustCompile(`\[(\d)\].*?[Mm]icrophone`)
	matches := re.FindStringSubmatch(ffmpegOutput)	
	if (len(matches) == 2) {
		return matches[1]
	}
	return ""
}